This application claims priority to Japanese Patent Application No. 2003-297319 filed 21 Aug. 2003, the content of which is incorporated herein by reference in its entirety.
The present invention relates to intake air amount control apparatuses and methods for internal combustion engines having a variable valve timing system and a valve operating angle variable system.
An internal combustion engine having a variable valve system that varies a valve operating state has been proposed. The valve operating state indicates valve timing, valve lift amount, and valve operating angle of an intake valve or an exhaust valve. Thus, the variable valve system varies the valve operating state by advancing or retarding the valve timing of the intake valve or exhaust valve, as well as varying the valve lift amount and the valve operating angle of the intake valve or exhaust valve.
The valve operating state greatly affects the performance of the engine. Therefore, if adjustment of the valve operating state is hampered by a problem occurring in the variable valve system, the engine must be switched to an engine safety mode immediately, ensuring that the engine operation is maintained as needed.
Japanese National-Phase Laid-Open Patent Publication No. 2002-542421 describes a technique regarding the engine safety mode. In accordance with the technique, if the intake air amount is adjusted by varying the valve operating angle of the intake valve and a problem occurs in the adjustment, the valve operating angle is fixed at a predetermined value. The intake air amount is adjusted by a throttle valve provided in an air intake system.
In accordance with Japanese Laid-Open Patent. Publication No. 2000-130196, if a problem occurs in an engine having a variable valve operating angle system and a variable valve timing system and controlling intake air amount with a throttle valve, valve overlapping is eliminated to ensure stable rotation of the engine. In this manner, the engine may be operated in the engine safety mode.
In an engine having a variable valve operating angle system for an intake valve and a variable valve timing system for an intake valve and/or an exhaust valve, intake air amount may be controlled by the variable valve operating angle system without employing a throttle valve.
In this structure, regardless of a problem caused in the variable valve timing system, the intake air amount may be adjusted through controlling of the valve operating angle of the intake valve, as long as the variable valve operating angle system functions normally. In other words, regardless of the problem hampering the valve timing adjustment, the engine is allowed to be operated in the engine safety mode.
However, it has been found that the engine performance may become unstable in certain cases, even though adjustment of the valve operating angle of the intake valve is maintained or the valve operating angle of the intake valve is fixed and the intake air amount is adjusted by a throttle valve. In this case, it is difficult to operate the engine in the engine safety mode.
This problem cannot be solved if the valve timing is invariable, as in Japanese National-Phase Laid-Open Patent Publication No. 2002-542421.
Further, Japanese Laid-Open Patent Publication No. 2000-130196 does not specify the controlling of the valve operating angle of the intake valve when a problem is detected in the valve timing adjustment. In addition, since the intake air amount is adjusted constantly by the throttle valve in this technique, the aforementioned problem cannot be addressed. It is thus unclear how the variable valve operating angle system for the intake valve is operated when a problem occurs in the valve timing adjustment.